This study used developmental rat submandibular gland, and studied alteration of hormonal control in exocrine cell.The endoportion of the submandibular gland is called the terminal tubule which is composed of an immature secretory unit. The terminal tubule has three different cells, the acinar cell, the proacinar cell and the terminal tubule cell. The proacinar cell is the precursor of the acinar cell, and all of the proacinar cells differentiate into the acinar cell by the second week after birth. Although the terminal tubule cell is the one which is recognized the most in the submandibular gland of the juvenile period, it does not exist in the adult submandibular gland. The formation of many cytoplasmic vacuoles were first identified in the terminal tubule cells of both sexes at day 18. The marked decrease of secretory granules and the release of vacuoles led to the transformation of the terminal tubules cells into the intercalated duct cells.The TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling) method showed positive reactions in a small number of cells in the terminal tubule cells. The number of positive cells increased until 28 days after birth. Electron microscopy revealed nuclear chromatin aggregation, suggesting apoptosis in terminal tubule cells 21 days or more after birth. These results suggest the close involvement of apoptosis in the regulation of cells constituting the submandibular gland in the postnatal growth of the rat submandibular gland.The immunohistochemical study of estrogen receptor and in situ hybridization study of estrogen receptor mRNA in order to identify the localization of estrogen receptor. In both study, a positive finding was recognized in the terminal tubule cell while no reaction was observed in another cells. The above study results have suggested that the terminal tubule cell is strongly controlled by estrogen.